Method for controlling of valve timing of continuous variable valve duration engine

ABSTRACT

A method for controlling valve timing for an engine includes: classifying a plurality of control regions depending on an engine speed and an engine load; applying a maximum duration to an intake valve and controlling an exhaust valve to limit a valve overlap in a first region; controlling the intake valve and the exhaust valve to maintain the maximum duration in a second region; advancing an intake valve closing (IVC) timing and an exhaust valve closing (EVC) timing in a third region; approaching the IVC timing to a bottom dead center (BDC) in a fourth region; controlling a throttle valve to be fully opened, advancing an intake valve opening (IVO) timing before a top dead center (TDC), and controlling the IVC timing to be a predetermined value after the BDC in a fifth region; and controlling the throttle valve to be fully opened and advancing the IVC timing in a sixth region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/258,035, filed on Sep. 6, 2016, and claims priority to andthe benefit of Korean Patent Application Nos. 10-2015-0177464, filed onDec. 11, 2015, and 10-2017-0154705, filed on Nov. 20, 2017, the entiretyof each of which are incorporated herein by reference.

FIELD

The present disclosure relates to a system and a method for controllingvalve timing of a continuous variable valve duration engine.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

An internal combustion engine combusts mixed gas in which fuel and airare mixed at a predetermined ratio through a set ignition mode togenerate power by using explosion pressure.

Generally, a camshaft is driven by a timing belt connected with acrankshaft that converts linear motion of a cylinder by the explosionpressure into rotating motion to actuate an intake valve and an exhaustvalve, and while the intake valve is opened, air is suctioned into acombustion chamber, and while an exhaust valve is opened, gas which iscombusted in the combustion chamber is exhausted.

To improve the operations of the intake valve and the exhaust valve andthereby improve engine performance, a valve lift and a valveopening/closing time (timing) should be controlled according to arotational speed or load of an engine. Therefore, a continuous variablevalve duration (CVVD) device controlling the opening duration of anintake valve and an exhaust valve of the engine and a continuousvariable valve timing (CVVT) device controlling the opening and closingtiming of the intake valve and the exhaust valve of the engine have beendeveloped.

The CVVD device may control opening duration of the valves. In addition,the CVVT device may advance or retard the opening or closing timing ofthe valves in a state that the opening duration of the valve is fixed.That is, if the opening timing of the valve is determined, the closingtiming is automatically determined according to the opening duration ofthe valve.

However, in case of combining the CVVD device and the CVVT device, boththe opening duration and timing of the valve should be simultaneouslycontrolled.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the present disclosureand therefore it may contain information that does not form the priorart that is already known to a person of ordinary skill in the art.

SUMMARY

The present disclosure provides a system and a method for controllingvalve timing of a continuous variable valve duration engine thatsimultaneously controls duration and timing of the valve being equippedwith a continuous variable valve duration device and a continuousvariable valve timing device disposed on an intake valve side andequipped with a continuous variable valve duration device on an exhaustvalve side of a turbo engine vehicle by independently controlling anopening and closing timing of an intake valve and an exhaust valve.

One form of the present disclosure, a method for controlling intake andexhaust valves of an engine may include: controlling, by an intakecontinuous variable valve timing (CVVT) device, opening and closingtimings of the intake valve; determining, by a controller, a targetopening duration of the intake valve, a target opening duration of theexhaust valve, and at least one of a target opening timing or a targetclosing timing of the intake valve and the exhaust valve, based on anengine load and an engine speed; modifying, by an intake continuousvariable valve duration (CVVD) device, current opening and closingtimings of the intake valve based on the target opening duration of theintake valve; modifying, by an exhaust CVVD device, current opening andclosing timings of the exhaust valve based on the target openingduration of the exhaust valve; advancing, by the intake CVVD device, thecurrent opening timing of the intake valve while simultaneouslyretarding the current closing timing of the intake valve by apredetermined value, or retarding the current opening timing of theintake valve while simultaneously advancing the current closing timingof the intake valve by a predetermined value, based on the targetopening duration of the intake valve; and advancing, by the exhaust CVVDdevice, the current opening timing of the exhaust valve whilesimultaneously retarding the current closing timing of the exhaust valveby a predetermined value, or retarding the current opening timing of theexhaust valve while simultaneously advancing the current closing timingof the exhaust valve by a predetermined value, based on the targetopening duration of the exhaust valve.

In particular, the intake CVVD device advances the current openingtiming of the intake valve while simultaneously retarding the currentclosing timing of the intake valve when the target opening duration ofthe intake valve is longer than a duration between the current openingtiming and current closing timing of the intake valve.

The intake CVVD device retards the current opening timing of the intakevalve while simultaneously advancing the current closing timing of theintake valve when the target opening duration of the intake valve isshorter than a duration between the current opening timing and currentclosing timing of the intake valve.

The exhaust CVVD device advances the current opening timing of theexhaust valve while simultaneously retarding the current closing timingof the exhaust valve when the target opening duration of the exhaustvalve is longer than a duration between the current opening timing andcurrent closing timing of the exhaust valve.

The exhaust CVVD device retards the current opening timing of theexhaust valve while simultaneously advancing the current closing timingof the exhaust valve when the target opening duration of the exhaustvalve is shorter than a duration between the current opening timing andcurrent closing timing of the exhaust valve.

The method further includes the step of adjusting, by the intake CVVTdevice, the current opening and closing timings of the intake valve tothe target opening and closing timings of the intake valve,respectively.

The method of further includes the step of adjusting, by the exhaustCVVT device, the current opening and closing timings of the exhaustvalve to the target opening and closing timings of the exhaust valve,respectively.

During the step of determining the target opening duration of the intakevalve, the controller sets the target opening duration of the intakevalve to a first intake opening duration in a first control region wherethe engine load is between first and second predetermined loads, and thecontroller controls the intake CVVD device to adjust a current intakeopening duration to the first opening duration and controls the exhaustvalve to limit a valve overlap in the first control region.

In one form, a valve overlap is limited by fixing the current openingand closing timings of the intake valve and by setting the closingtiming of the exhaust valve to be a maximum value to maintain combustionstability in the first control region

During the step of determining the target opening duration of the intakevalve, the controller sets the target opening duration of the intakevalve to a second intake opening duration in a second control regionwhere the engine load is greater than the second predetermined load andequal to or less than a third predetermined load, and the controllercontrols the intake CVVD device to adjust the current intake openingduration to the second intake opening duration, and wherein the secondintake opening duration is equal to or longer than the first intakeopening duration.

The method further includes the step of determining, by the controller,a third control region where the engine load is greater than the thirdpredetermined load and less than a fourth predetermined load and theengine speed is between first and second predetermined speeds, or wherethe engine load is greater than the third predetermined load and equalto or less than a fifth predetermined load and the engine speed isbetween the second predetermined speed and a third predetermined speed;advancing, by the intake CVVT device, the current closing timing of theintake valve by a predetermined angle in the third control region; andadvancing, by the exhaust CVVD device, the current closing timing of theexhaust valve by a predetermined angle in the third control region.

The method further includes the step of advancing the current closingtiming of the intake valve to be approximately at a bottom dead center(BDC) when the engine speed less than or equal to a predetermined speed;and advancing the current closing timing of the intake valve to be afterthe BDC when the engine speed is greater than the predetermined speed inthe third control region.

The method may further have the step of determining a fourth controlregion, by the controller, where the engine load is greater than afourth predetermined load and equal to or less than a fifthpredetermined load and the engine speed is equal to or greater than afirst predetermined speed and equal to or less than a secondpredetermined speed; and approaching, by the intake CVVT device, thecurrent closing timing of the intake valve to be approximately at abottom dead center (BDC) in the fourth control region.

The method further includes the step of approaching the current closingtiming of the intake valve to a top dead center (TDC) by the intake CVVTdevice, and approaching the current closing timing of the exhaust valveto the TDC by the exhaust CVVD device in the fourth control region.

The method further includes the step of determining, by the controller,a fifth control region where the engine load is greater than a fifthpredetermined load and equal to or less than a maximum engine load andthe engine speed is between first and second predetermined speeds;controlling, by the controller, a throttle valve to be fully opened; andadvancing, by the intake CVVT device, the current opening timing of theintake valve to be before a top dead center (TDC), and controlling thecurrent closing timing of the intake valve to be a predetermined valueafter a bottom dead center in the fifth control region.

The method further includes the step of determining, by the controller,a sixth control region where the engine load is greater than a fifthpredetermined load and equal to or less than a maximum engine load andthe engine speed is greater than a second predetermined speed and equalto or less than a third predetermined speed; controlling, by thecontroller, a throttle valve to be fully opened; and advancing, by theintake CVVT device, the current closing timing of the intake valve by apredetermined angle in the sixth control region.

The method further includes the step of approaching the current closingtiming of the exhaust valve to a top dead center to inhibit a valveoverlap in the sixth control region.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure;

FIG. 2 is a perspective view showing a continuous variable valveduration device and a continuous variable valve timing device which aredisposed on an intake valve side, and a continuous variable valveduration device disposed on an exhaust valve side according to one formof the present disclosure;

FIG. 3 is a side view of a continuous variable valve duration deviceassembled with a continuous variable valve timing device which isdisposed on intake valve and exhaust valve sides;

FIG. 4 is a partial view of an inner wheel and a cam unit of acontinuous variable valve duration device in one form;

FIGS. 5A-5C are views illustrating the operation of a continuousvariable valve duration device in FIG. 4;

FIGS. 6A and 6B are views illustrating a cam slot of a continuousvariable valve duration device in exemplary forms;

FIGS. 7A-7C are valve profiles of a continuous variable valve durationdevice in one form;

FIGS. 8A-8D illustrate a change of an opening duration and opening andclosing timings of a valve;

FIGS. 9A and 9B are flowcharts showing a method for controlling valvetiming of a continuous variable valve duration engine according to oneform of the present disclosure;

FIG. 10 is a schematic diagram illustrating control regions in one form;

FIGS. 11A-11C are drawings showing duration, opening timing, and closingtiming of an intake valve depending on an engine load and an enginespeed according to the present disclosure; and

FIGS. 12A-12C are drawings showing duration, opening timing, and closingtiming of an exhaust valve depending on an engine load and an enginespeed according to the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

As those skilled in the art would realize, the described forms may bemodified in various different ways, all without departing from thespirit or scope of the present disclosure.

Throughout this specification and the claims which follow, unlessexplicitly described to the contrary, the word “comprise” and variationssuch as “comprises” or “comprising” will be understood to imply theinclusion of stated elements but not the exclusion of any otherelements.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general includinghybrid vehicles, plug-in hybrid electric vehicles, and other alternativefuel vehicles (e.g., fuels derived from resources other than petroleum).As referred to herein, a hybrid electric vehicle is a vehicle that hastwo or more sources of power, for example a gasoline-powered andelectric-powered vehicle.

Additionally, it is understood that some of the methods may be executedby at least one controller. The term controller refers to a hardwaredevice that includes a memory and a processor configured to execute oneor more steps that should be interpreted as its algorithmic structure.The memory is configured to store algorithmic steps, and the processoris specifically configured to execute said algorithmic steps to performone or more processes which are described further below.

Furthermore, the control logic of the present disclosure may be embodiedas non-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor, acontroller, or the like. Examples of computer readable media include,but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetictapes, floppy disks, flash drives, smart cards, and optical data storagedevices. The computer readable recording medium can also be distributedin network coupled computer systems so that the computer readable mediais stored and executed in a distributed fashion, e.g., by a telematicsserver or a controller area network (CAN).

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure.

As shown in FIG. 1, a system for controlling valve timing of acontinuous variable valve duration engine includes: a data detector 100,a camshaft position sensor 120, a controller 300, an intake continuousvariable valve duration (CVVD) device 400, an intake continuous variablevalve timing (CVVT) device 450, and an exhaust continuous variable valveduration (CVVD) device 500.

The data detector 100 detects data related to a running state of thevehicle for controlling the CVVD devices and the CVVT devices, andincludes a vehicle speed sensor 111, an engine speed sensor 112, an oiltemperature sensor 113, an air flow sensor 114, and an accelerator pedalposition sensor (APS) 115, although other sensors or systems may beemployed to detect or determine the desired data.

The vehicle speed sensor 111 detects a vehicle speed, transmits acorresponding signal to the controller 300, and may be mounted at awheel of the vehicle.

The engine speed sensor 112 detects a rotation speed of the engine froma change in phase of a crankshaft or camshaft, and transmits acorresponding signal to the controller 300.

The oil temperature sensor (OTS) 113 detects temperature of oil flowingthrough an oil control valve (OCV), and transmits a corresponding signalto the controller 300.

The oil temperature detected by the oil temperature sensor 113 may bedetermined by measuring a coolant temperature using a coolanttemperature sensor mounted at a coolant passage of an intake manifold.Therefore, in one form, the oil temperature sensor 113 may include acoolant temperature sensor, and the oil temperature should be understoodto include the coolant temperature.

The air flow sensor 114 detects an air amount drawn into the intakemanifold, and transmits a corresponding signal to the controller 300.

The accelerator pedal position sensor (APS) 115 detects a degree inwhich a driver pushes an accelerator pedal, and transmits acorresponding signal to the controller 300. The position value of theaccelerator pedal may be 100% when the accelerator pedal is pressedfully, and the position value of the accelerator pedal may be 0% whenthe accelerator pedal is not pressed at all.

A throttle valve position sensor (TPS) that is mounted on an intakepassage may be used instead of the accelerator pedal position sensor115. Therefore, in one form, the accelerator pedal position sensor 115may include a throttle valve position sensor, and the position value ofthe accelerator pedal should be understood to include an opening valueof the throttle valve.

The camshaft position sensor 120 detects a change of a camshaft angle,and transmits a corresponding signal to the controller 300.

Referring to FIG. 2, a continuous variable valve duration device and acontinuous variable valve timing device are mounted on the intake valveside, and the continuous variable valve duration device is mounted onthe exhaust valve side through a fixed opening device. Therefore, anexhaust valve opening (EVO) timing is fixed in the one form of thepresent disclosure. For example, the EVO timing may be fixed at an anglea before bottom dead center of approximately 40 to 50 degrees at most ofpart load regions so as to be advantageous fuel efficiency.

The intake continuous variable valve duration (CVVD) device 400 controlsan intake valve opening duration of the engine according to a signal ofthe controller 300, and the exhaust continuous variable valve duration(CVVD) device 500 controls an exhaust valve opening duration of theengine according to a signal of the controller 300.

The intake continuously variable valve timing (CVVT) device 450 controlsopening and closing timing of the intake valve according to a signal ofthe controller 300.

FIG. 3 is a side view of the CVVD device (400, 500) applied to theintake and exhaust valves in another form as assembled with valves 200operating with cylinders 201, 202, 203, 204. In particular, the intakeCVVD device 400 is assembled with the intake CVVT device 450. In oneform, two cams 71 and 72 may be formed on first and second cam portions70 a and 70 b, and a cam cap engaging portion 76 may be formed betweenthe cams 71 and 72 and supported by a cam cap 40. The valve 200 isopened and closed by being in contact with the cams 71 and 72.

As illustrated in FIG. 3, the CVVD device includes: a cam unit 70 inwhich a cam 71 is formed and into which a cam shaft 30 is inserted; aninner wheel 80 to transfer the rotation of the cam shaft 30 to the camunit 70 (See, in FIG. 4); a wheel housing 90 in which the inner wheel 80rotates and movable in a direction perpendicular to the camshaft 30; aguide shaft 132 having a guide thread and provided in a directionperpendicular to the camshaft 30, the guide shaft mounted by a guidebracket 134; a worm wheel 50 having an inner thread engaged with theguide thread and disposed inside the wheel housing 90; and a controlshaft 102 formed with a control worm 104 meshing with the worm wheel 50.The control worm 104 is engaged with an outer thread formed on the outerside of the worm wheel 50. The CVVD device further includes a slidingshaft 135 fixed to the guide bracket 134 and guiding the movement of thewheel housing 90.

FIG. 4 is a partial view of the inner wheel 80 and the cam unit 70 ofthe CVVD device of the FIG. 3. Referring to FIG. 4, First and secondsliding holes 86 and 88 are formed in the inner wheel 80, and a cam slot74 is formed in the cam unit 70.

The CVVD device further includes: a roller wheel 60 inserted into thefirst sliding hole 86 allowing the roller wheel 60 to rotate; and aroller cam 82 inserted into the cam slot 74 and the second sliding hole88. The roller cam 82 may slide in the cam slot 74 and rotate in thesecond sliding hole 88.

The roller cam 82 includes: a roller cam body 82 a slidably insertedinto the cam slot 74 and a roller cam head 82 b rotatably inserted intothe second sliding hole 88.

The roller wheel 60 includes: a wheel body 62 slidably inserted into thecamshaft 30 and a wheel head 64 rotatably inserted into the firstsliding hole 86. A cam shaft hole 34 is formed in the camshaft 30 and awheel body 62 of the roller wheel 60 is movably inserted into thecamshaft hole 34. The structure and operation of the CVVD devicediscussed above applies to both the intake and exhaust CVVD devices 400,500.

FIGS. 5A-5C illustrate the operation of the CVVD device. FIG. 5Aillustrates a neutral state in which the rotational center of thecamshaft 30 and the cam unit 70 coincide with each other. In this case,the cams 71 and 72 rotate at the same speed as the camshaft 30. When thecontroller 300 applies a control signal based on engine load and/orengine speed, a control motor 106 rotates the control shaft 102. Then,the control worm 104 rotates the worm wheel 50 which in turn rotates andmoves along the guide thread formed on the guide shaft 132.

As a result, the worm wheel 50 causes a change to a position of thewheel housing 90 relative to the cam shaft 30. As illustrated in FIGS.5B and 5C, when the position of the wheel housing 90 moves in onedirection with respect to the center of rotation of the camshaft 30, therotational speed of the cams 71, 72 with respect to the camshaft 30 arechanged in accordance with their phases. FIG. 7A and FIG. 8B aredrawings showing a valve profile illustrating valve opening durationchange by the operation of the CVVD device (i.e., intake CVVD device,exhaust CVVD device). The solid line represents a general valve profile(e.g., a current opening duration), and the dotted line shows the valveprofile as a short opening duration (e.g., a target opening duration inFIG. 8B) is applied. FIG. 8A illustrates a changed valve profile whenthe long opening duration is applied by the CVVD device. The controller300 determines a target opening duration based on an engine load and anengine speed and controls the CVVD device (i.e., the intake CVVD device,the exhaust CVVD device) to modify current opening and closing timingsof the valve based on the target opening duration.

More specifically, as illustrated in FIG. 8B, the CVVD device may retardthe current opening timing of the intake valve while simultaneouslyadvancing the current closing timing of the intake valve to shorten theopening duration according to a predetermined value provided by thecontroller 300. When the controller applies a longer opening duration(i.e., a target opening duration) than the current opening duration, asillustrated in FIG. 8A, the CVVD device may advance the current openingtiming of the intake valve while simultaneously retarding the currentclosing timing of the intake vale so that the modified opening durationbecomes longer than the current opening duration. The same operationdiscussed above applies to the exhaust valve to control an openingduration of the exhaust valve.

FIGS. 8C and 8D illustrate the relationship between the operation of theCVVD device and the CVVT device. As discussed above, the CVVD device maychange the opening duration of a valve (e.g., intake or exhaust valve)whereas the CVVT device may shift a valve profile according to a targetopening and/or a target closing timings without change to the period ofthe valve opening duration. It should be noted that the changing openingduration by the CVVD device may occur after changing valve openingand/or closing timings of intake or exhaust valves by the CVVT device.In another form, the operation of the CVVT device to change the openingand closing timings may occur after the operation of the CVVD device. Instill another form, the operation of the CVVD and CVVT devices mayperform simultaneously to change the opening duration and the timing ofopening and closing of intake or exhaust valves.

FIGS. 6A and 6B illustrate a view of the cam slot 74 a, 74 b of the CVVDdevice, and FIGS. 7A-7C illustrate valve profiles of the CVVD device inexemplary forms of the present disclosure.

Referring to FIGS. 6A-6B, the cam slot 74 a may be formed in an advancedposition relative to the cam 71, 72, or in another form the cam slot 74b may be formed in a retarded position relative to the cam 71, 72. Inanother form, the cam slot 74 a, 74 b may be formed to have the samephase as the lobe of the cam 71, 72. These variations are enable torealize various valve profiles. Based on the position of the cam slot 74a, 74 b, and a contact position between the cam and the correspondingvalve (i.e., the intake valve, the exhaust valve), the opening andclosing timings of the intake valve (or exhaust valve) may vary. FIG. 7Bshows that the CVVD device may advance (for a short opening duration) orretard the current closing timing (for a long opening duration) of thecorresponding valve (i.e., intake valve, exhaust valve) by apredetermined value based on the target opening duration of the intakevalve or exhaust valve while maintaining the current opening timing ofthe intake valve or the exhaust valve. In another form, as illustratedin FIG. 7C, the CVVD device may advance (for a long opening duration) orretard (for a short opening duration) the current opening timing of theintake valve or the exhaust valve by a predetermined value based on thetarget opening duration of the intake valve or the exhaust valve whilemaintaining the current closing timing of the intake valve or theexhaust valve.

The controller 30 may classify a plurality of control regions dependingon an engine speed and an engine load based on signals from the datadetector 100 and camshaft position sensor 120, and control the intakeCVVD device 400, the exhaust CVVD device 500 and the intake CVVT device450. Herein, the plurality of control regions may be classified into sixregions.

The controller 300 may apply a maximum duration (i.e., a target openingduration) to the intake valve and control to limit a valve overlap byusing the exhaust valve in a first region, apply the maximum duration tothe intake and exhaust valves in a second region, and advance an intakevalve closing (IVC) timing and exhaust valve closing (EVC) timing in thethird region. And the controller 300 may approach the intake valveclosing (IVC) timing to a bottom dead center (BDC) in a fourth region,control a wide open throttle valve (WOT) and advance an intake valveopening (IVO) timing before a top dead center (TDC) and control anintake valve closing (IVC) timing after the bottom dead center (BDC) ina fifth region, and control a wide open throttle valve (WOT) and advancean intake valve closing (IVC) timing in a sixth region.

For these purposes, the controller 300 may be implemented as at leastone processor that is operated by a predetermined program, and thepredetermined program may be programmed in order to perform each step ofa method for controlling valve timing of a continuous variable valveduration engine according to one form of the present disclosure.

Various forms described herein may be implemented within a recordingmedium that may be read by a computer or a similar device by usingsoftware, hardware, or a combination thereof, for example.

The hardware of the forms described herein may be implemented by usingat least one of application specific integrated circuits (ASICs),digital signal processors (DSPs), digital signal processing devices(DSPDs), programmable logic devices (PLDs), field programmable gatearrays (FPGAs), processors, controllers, micro-controllers,microprocessors, and electrical units designed to perform any otherfunctions.

The software such as procedures and functions of the forms described inthe present disclosure may be implemented by separate software modules.Each of the software modules may perform one or more functions andoperations described in the present disclosure. A software code may beimplemented by a software application written in an appropriate programlanguage.

Hereinafter, a method for controlling valve timing of a continuousvariable valve duration engine according to one form of the presentdisclosure will be described in detail with reference to FIG. 9A to FIG.12C.

FIG. 9A and FIG. 9B are flowcharts showing a method for controllingvalve timing of a continuous variable valve duration engine, and FIG. 10is a schematic block diagram of showing control regions based on engineload (e.g., engine torque) and engine speed.

In addition, FIGS. 11A-11C are drawings showing duration, openingtiming, and closing timing of an intake valve depending on an engineload and an engine speed, and FIGS. 12A-12C are drawings showingduration, opening timing, and closing timing of an exhaust valvedepending on an engine load and an engine speed.

In the FIGS. 11A-11C and FIGS. 12A-12C, an IVD map and an EVD mapindicate a crank angle, an IVO timing map indicates an angle before atop dead center, an IVC timing map indicates an angle after a bottomdead center, an EVO timing map indicates an angle before a bottom deadcenter, and an EVC timing map indicates an angle after a top deadcenter.

As shown in FIG. 9A and FIG. 9B, a method for controlling valve timingof a continuous variable valve duration engine starts with classifying aplurality of control regions depending on an engine speed and an engineload by the controller 30 o at step S100. The control region may bedivided into six control regions (e.g., first, second, third, fourth,fifth and sixth control regions).

The first to sixth control regions are indicated in FIG. 10, and FIG.11A to FIG. 12C in more detail. FIG. 10 schematically describes thecontrol regions based on the engine load (e.g., engine torque) andengine speed (e.g., revolutions per minutes “rpm”). However, the controlregions may vary based on engine type or engine size. Mixed control maybe performed at the boundary of each region to minimize the controlimpact of the engine. Accordingly, the range of each region shown in thepresent application is exemplary, and the classification of each regionmay be varied.

The controller 300 may determine control regions as a first controlregion (namely, {circle around (1)} an idling region or a low-loadcondition) when the engine load is between a first predetermined load(e.g., a minimum engine torque) and a second predetermined load, asecond control region (namely, {circle around (2)} an mid-loadcondition) when the engine load is greater than the second predeterminedload and equal to or less than a third predetermined load, and a thirdcontrol region (namely, {circle around (3)} a high-load condition) wherethe engine load is greater than the third predetermined load and lessthan a fourth predetermined load and the engine speed is between a firstpredetermined speed (e.g., an idle rpm) and a second predeterminedspeed, or where the engine load is greater than the third predeterminedload and equal to or less than a fifth predetermined load and the enginespeed is between the second predetermined speed and a thirdpredetermined speed (i.e., an engine maximum rpm).

In addition, the controller 300 may determine a fourth control region(namely, {circle around (4)} a low-speed and high-load condition) whenthe engine load is greater than the fourth predetermined load and equalto or less than a fifth predetermined load and the engine speed is equalto or greater than the first predetermined speed and equal to or lessthan the second predetermined speed, a fifth control region (namely,{circle around (5)} a low speed-wide open throttle “WOT” condition) whenthe engine load is greater than the fifth predetermined load and equalto or less than a maximum engine load and the engine speed is betweenthe first and second predetermined speeds, and a sixth control region(namely, {circle around (6)} an mid-high speed-WOT condition) when theengine load is greater than the fifth predetermined load and equal to orless than the maximum engine load and the engine speed is greater thanthe second predetermined speed and equal to or less than a thirdpredetermined speed (e.g., an engine maximum rpm).

Referring to FIG. 10, the first predetermined load (e.g., a minimumengine torque) is measured when a input from the APS is zero “0,” andthe second to fifth predetermined loads, and the second and thirdpredetermined engine speeds may be calculated by the followingequations:Second predetermined load=min_L+(⅕)×(max_L−min_L);Third predetermined load=min_L+(⅖)×(max_L−min_L);Fourth predetermine load=min_L+(½)×(max_L−min_L);Fifth predetermined load=min_L+(⅘)×(max_L−min_L);Second predetermined engine speed=min_S+( 3/10)×(max_S−min_S); andThird predetermined engine speed=max_S,

where, min_L is the minimum engine torque; max_L is a maximum enginetorque; min_S is a minimum engine rpm (e.g., Idle rpm); and max_S is amaximum engine rpm.

Meanwhile, referring to FIGS. 11A-11C and FIGS. 12A-12C, a crank angleis marked in an intake valve duration (IVD) map and an exhaust valveduration (EVD) map, which indicating the opening time of the intakevalve and exhaust valve. For example, regarding the IVD map in the FIG.11A, a curved line written as a number 200 at inner side of the fourthregion means that the crank angle is approximately 200 degrees, a curvedlined marked as a number 220 at outer side of the number 200 means thatthe crank angle is approximately 220 degrees. Although not shown in thedrawing, the crank angle which is more than approximately 200 degreesand less than approximately 220 degrees is positioned between the curvedline of the number 200 and the curved line of the number 220.

In addition, a unit of number designated in an intake valve opening(IVO) timing map is before a top dead center (TDC), a unit of numberdesignated in an intake valve closing (IVC) timing map is after a bottomdead center (BDC), a unit of number designated in an exhaust valveopening (EVO) timing map is before BDC, and a unit of number designatedin an exhaust valve closing (EVC) map is after TDC.

Each region and curved line in the FIGS. 11A-11C and FIGS. 12A-12C arean exemplary form of the present disclosure, it may be modified withinthe technical idea and scope of the present disclosure.

Referring to FIG. 9A to FIG. 12C, the control regions are determinedaccording to the engine speed and load in the step of S100. After that,the controller 300 determines whether the engine state is under thefirst region at step S110.

In the step of S110, if the engine load is between first and secondpredetermined loads, the controller 300 determines that the engine stateis under the first region. At this time, the controller 300 applies amaximum duration or a first intake opening duration to the intake valveand controls the valve overlap between the exhaust valve and intakevalve at step S120. The valve overlap is a state where the intake valveis opened and the exhaust valve is not closed yet.

In other words, when the engine is under low load, then the controller300 may control both the intake valve opening (IVO) timing and theintake valve closing (IVC) timing being fixed such that the intake valvehas a maximum duration value. In other words, the controller 300controls the intake CVVD device to adjust a current opening duration tothe first intake opening duration by advancing the IVO timing andretarding the IVC timing.

As shown in FIGS. 11A-11C, the first region may be fixed approximately 0to 10 degrees before TDC in the IVO timing map and fixed approximately100 to 110 degrees after BDC in the IVC timing map.

In addition, the controller 300 may limit the overlap by setting the EVCtiming as a maximum value to maintain combustion stability.

When the current engine state does not belong to the first region at thestep S110, the controller 300 determines whether the current enginestate belongs to the second region at step S130. However, each of thecontrol regions may be determined immediately by the controller 300based on the engine load and/or engine speed.

When the current engine state belongs to the second region where theengine load is greater than the second predetermined load and equal toor less than the third predetermined load, the controller 300 controlsthe intake valve and the exhaust valve to maintain the maximum durationat step S140. In another form, the controller 300 may set the targetopening duration of the intake valve to a second intake opening durationin the second control region, and the controller 300 controls the intakeCVVD device to adjust the current opening duration to the second intakeopening duration. The second opening duration may be set to be equal toor longer than the first intake opening duration.

The controller 300 may maintain the maximum duration of the exhaustvalve by retarding the EVC timing as the engine load increases. Herein,the controller 300 may use the maximum duration of the exhaust by fixingthe IVO timing and the IVC timing with the maximum duration of theintake used in the first region.

Meanwhile, a manifold absolute pressure (MAP) of the intake which is apressure difference between atmospheric pressure and pressure of theintake manifold should be constantly maintained in the natural aspiratedengine, on the contrary, it may not need to control in the turbo engineaccording to one form of the present disclosure because pressure of theintake manifold is greater than atmospheric pressure due to boost.

When the engine load is greater than the third predetermined load andless than a fourth predetermined load and the engine speed is betweenfirst and second predetermined speeds, or when the engine load isgreater than the third predetermined load and equal to or less than afifth predetermined load and the engine speed is between the secondpredetermined speed and a third predetermined speed, the controller 300determines whether the current engine state belongs to the third regionat step S150.

When the current engine state belongs to the third region at the stepS150, the controller 300 advances the IVC timing and the EVC timing atstep S160.

Since the IVC timing is controlled at the LIVC position (for example, anangle approximately 100-110 of degrees after a bottom dead center) inthe first and second regions, knocking may be generated as the engineload is increased. Accordingly, fuel efficiency may be deteriorated asboost pressure is increased and knocking is deteriorated. In order toinhibit or prevent effect as described above, the controller 300advances the IVC timing.

At this time, as shown in FIGS. 11A-11C, the controller 300 may rapidlyadvance the IVC timing close to a bottom dead center when the enginespeed is less than or equal to a predetermined speed, and may slowlyadvance the IVC timing at an angle of approximately 30 to 50 degreesafter the bottom dead center when the engine speed is greater than thepredetermined speed so as to reflect characteristic of the turbo engine.The predetermined speed may be approximately 1500 rpm.

In addition, as shown in FIGS. 12A-120, the controller 300 may advancethe EVC timing close to a top dead center since the EVC timing ispositioned at the maximum value of the overlap in the first and secondregions.

When the current engine state does not belong to the third region at thestep S150, the controller 300 determines whether the current enginestate belongs to the fourth region at step S170. In another form, thecontroller 300 may determine the condition for the fourth control regionwithout performing the step of determining the first, second and thirdcontrol regions.

If the engine state is under the fourth region in the S170, thecontroller 300 controls the IVC timing close to the BDC at step S180.

The fourth region may be a low boost region (or, a low-speed andhigh-load region) that the engine load is greater than the fourthpredetermined load and equal to or less than the fifth predeterminedload and the engine speed is greater than or equal to the firstpredetermined speed and less than the second predetermined speed. Forexample, the first predetermined speed (i.e., an idle rpm) may beapproximately 1500 rpm or less, and the second predetermined speed maybe approximately 2500 rpm.

The controller 300 controls the IVC timing close to BDC in the fourthregion, thereby improving fuel efficiency. In addition, the controller300 may inhibit or prevent the overlap by controlling the IVO timing andthe EVC timing close to top dead center. Accordingly, a short intakeduration (e.g., approximately 180 degrees) may be used in the fourthregion.

When the engine load is greater than the fifth predetermined load andequal to or less than a maximum engine load and the engine speed isbetween the first and second predetermined speeds, the controller 300determines that the current engine state belongs to the fifth region atstep S190.

When the current engine state belongs to the fifth region at the stepS190, the controller 300 fully opens a throttle valve, advances the IVOtiming before the TDC and controls the IVC timing after the BDC at stepS200.

In the turbo engine, if the throttle valve is controlled to be wide open(Wide Open Throttle “WOT”) when the engine speed is equal to or greaterthan the first predetermined speed (e.g., an idling rpm) and less thanthe second predetermined speed (e.g., 2500 rpm), intake port pressurebecomes higher than exhaust port pressure by boosting. Therefore, effectof a scavenging phenomenon which emits combustion gas of the exhaust isprominent in the turbo engine compared to a natural aspirated engine.Accordingly, as shown in FIGS. 11A-11C, the controller 300 may advancethe IVO timing at an angle of approximately 20 to 40 degrees before theTDC to generate the scavenging, and control the IVC timing at angle ofapproximately 0 to 20 degrees after the BDC. More specifically, thefresh air at a higher pressure than that of the burned gases (combustiongas) scavenges the burned gases and evacuates them through the exhaustvalve, thus filling the space freed by these gases.

Although the EVO timing is retarded after the BDC in order to increasethe scavenging phenomenon through exhaust interference reduction, theEVO timing is fixed before the BDC in one form of the presentdisclosure. Accordingly, the present disclosure may be appropriate for athree-cylinder engine insignificantly influenced by the exhaustinterference than a four-cylinder greatly influenced by the exhaustinterference.

When the current engine state is greater than the fifth predeterminedload and equal to or less than the maximum engine load and the enginespeed is greater than the second predetermined speed and less than athird predetermined speed (e.g., a maximum rpm of an engine), thecontroller 300 determines whether the current engine state belongs tothe sixth region at step S210.

When the current engine state belongs to the sixth region at the stepS210, the controller 300 fully opens a throttle valve and advances theIVC timing at step S220.

When the engine speed is greater than a predetermined speed (e.g.,approximately 3500 rpm) in the sixth region, the scavenging phenomenondisappears because exhaust port pressure is much higher than intake portpressure. In this case, since the EVO timing is fixed to increase theexhaust pumping, the valve overlap can be inhibited or prevented byapproaching the EVC timing to the TDC, as shown in FIGS. 12A-12C.

Meanwhile, when WOT control is performed at a high speed condition, theknocking is rarely generated in the natural aspiration engine, on thecontrary, the knocking may be deteriorated in the turbo engine. Thus, asshown in FIGS. 11A-11C, the controller 300 may advance the IVC timingwithin an angle of approximately 50 degrees after BDC to reduce knockingby decreasing boost pressure.

As described above, according to the present disclosure, duration andtiming of the continuous variable valve are simultaneously controlled,so the engine may be controlled under desired conditions.

That is, since opening timing and closing timing of the intake valve andthe exhaust valve are appropriately controlled, the fuel efficiencyunder a partial load condition and engine performance under a high loadcondition are improved. In addition, a starting fuel amount may bereduced by increasing a valid compression ratio, and exhaust gas may bereduced by shortening time for heating a catalyst.

In addition, by omitting the continuously variable valve timing deviceat the exhaust valve side, it is possible to reduce cost and avoid theproblem of valve timing control.

While this present disclosure has been described in connection with whatis presently considered to be practical exemplary forms, it is to beunderstood that the present disclosure is not limited to the disclosedforms. On the contrary, it is intended to cover various modificationsand equivalent arrangements included within the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for controlling intake and exhaustvalves of an engine, the method comprising: controlling, by an intakecontinuous variable valve timing (CVVT) device, opening and closingtimings of the intake valve; determining, by a controller, a targetopening duration of the intake valve, a target opening duration of theexhaust valve, and at least one of a target opening timing or a targetclosing timing of the intake valve and the exhaust valve, based on anengine load and an engine speed; modifying, by an intake continuousvariable valve duration (CVVD) device, current opening and closingtimings of the intake valve based on the target opening duration of theintake valve; modifying, by an exhaust CVVD device, current opening andclosing timings of the exhaust valve based on the target openingduration of the exhaust valve; advancing, by the intake CVVD device, thecurrent opening timing of the intake valve while simultaneouslyretarding the current closing timing of the intake valve by apredetermined value, or retarding the current opening timing of theintake valve while simultaneously advancing the current closing timingof the intake valve by a predetermined value, based on the targetopening duration of the intake valve; and advancing, by the exhaust CVVDdevice, the current opening timing of the exhaust valve whilesimultaneously retarding the current closing timing of the exhaust valveby a predetermined value when the target opening duration of the exhaustvalve is longer than a duration between the current opening timing andcurrent closing timing of the exhaust valve, or retarding the currentopening timing of the exhaust valve while simultaneously advancing thecurrent closing timing of the exhaust valve by a predetermined valuewhen the target opening duration of the exhaust valve is shorter thanthe duration between the current opening timing and current closingtiming of the exhaust valve.
 2. The method of claim 1, wherein theintake CVVD device advances the current opening timing of the intakevalve while simultaneously retarding the current closing timing of theintake valve when the target opening duration of the intake valve islonger than a duration between the current opening timing and currentclosing timing of the intake valve.
 3. The method of claim 1, whereinthe intake CVVD device retards the current opening timing of the intakevalve while simultaneously advancing the current closing timing of theintake valve when the target opening duration of the intake valve isshorter than a duration between the current opening timing and currentclosing timing of the intake valve.
 4. The method of claim 1, furthercomprising the step of adjusting, by the intake CVVT device, the currentopening and closing timings of the intake valve to the target openingand closing timings of the intake valve, respectively.
 5. The method ofclaim 1, further comprising the step of adjusting, by the exhaust CVVTdevice, the current opening and closing timings of the exhaust valve tothe target opening and closing timings of the exhaust valve,respectively.
 6. The method of claim 1, wherein, during the step ofdetermining the target opening duration of the intake valve, thecontroller sets the target opening duration of the intake valve to afirst intake opening duration in a first control region where the engineload is between first and second predetermined loads, and the controllercontrols the intake CVVD device to adjust a current intake openingduration to the first opening duration and controls the exhaust valve tolimit a valve overlap in the first control region.
 7. The method ofclaim 6, wherein a valve overlap is limited by fixing the currentopening and closing timings of the intake valve and by setting theclosing timing of the exhaust valve to be a maximum value to maintaincombustion stability in the first control region.
 8. The method of claim6, wherein, during the step of determining the target opening durationof the intake valve, the controller sets the target opening duration ofthe intake valve to a second intake opening duration in a second controlregion where the engine load is greater than the second predeterminedload and equal to or less than a third predetermined load, and thecontroller controls the intake CVVD device to adjust the current intakeopening duration to the second intake opening duration, and wherein thesecond intake opening duration is equal to or longer than the firstintake opening duration.
 9. The method of claim 8, further comprisingthe step of determining, by the controller, a third control region wherethe engine load is greater than the third predetermined load and lessthan a fourth predetermined load and the engine speed is between firstand second predetermined speeds, or where the engine load is greaterthan the third predetermined load and equal to or less than a fifthpredetermined load and the engine speed is between the secondpredetermined speed and a third predetermined speed; advancing, by theintake CVVT device, the current closing timing of the intake valve by apredetermined angle in the third control region; and advancing, by theexhaust CVVD device, the current closing timing of the exhaust valve bya predetermined angle in the third control region.
 10. The method ofclaim 9, further comprising the step of advancing the current closingtiming of the intake valve to be approximately at a bottom dead center(BDC) when the engine speed less than or equal to a predetermined speed;and advancing the current closing timing of the intake valve to be afterthe BDC when the engine speed is greater than the predetermined speed inthe third control region.
 11. The method of claim 1, further comprisingthe step of determining a fourth control region, by the controller,where the engine load is greater than a fourth predetermined load andequal to or less than a fifth predetermined load and the engine speed isequal to or greater than a first predetermined speed and equal to orless than a second predetermined speed; and approaching, by the intakeCVVT device, the current closing timing of the intake valve to beapproximately at a bottom dead center (BDC) in the fourth controlregion.
 12. The method of claim 11, further comprising the step ofapproaching the current closing timing of the intake valve to a top deadcenter (TDC) by the intake CVVT device, and approaching the currentclosing timing of the exhaust valve to the TDC by the exhaust CVVDdevice in the fourth control region.
 13. The method of claim 1, furthercomprising the step of determining, by the controller, a fifth controlregion where the engine load is greater than a fifth predetermined loadand equal to or less than a maximum engine load and the engine speed isbetween first and second predetermined speeds; controlling, by thecontroller, a throttle valve to be fully opened; and advancing, by theintake CVVT device, the current opening timing of the intake valve to bebefore a top dead center (TDC), and controlling the current closingtiming of the intake valve to be a predetermined value after a bottomdead center in the fifth control region.
 14. The method of claim 1,further comprising the step of determining, by the controller, a sixthcontrol region where the engine load is greater than a fifthpredetermined load and equal to or less than a maximum engine load andthe engine speed is greater than a second predetermined speed and equalto or less than a third predetermined speed; controlling, by thecontroller, a throttle valve to be fully opened; and advancing, by theintake CVVT device, the current closing timing of the intake valve by apredetermined angle in the sixth control region.
 15. The method of claim14, further comprising the step of approaching the current closingtiming of the exhaust valve to a top dead center to inhibit a valveoverlap in the sixth control region.